In a wide variety of activities involving the handling and deployment of objects, such as maneuvering a payload from a spacecraft bay to a deployment position or grappling a free-flying payload, a remotely operated manipulator system is usually provided. For almost all such applications, the grappling device or end effector associated with the manipulator arm is desirably of small size, light weight, and readily adaptable to handling payloads of various sizes, masses, and shapes. Although magnetic devices which incorporate permanent magnets have sometimes been used as attachment mechanisms in lieu of mechanical gripping devices because of their relative simplicity and other desirable features, these generally have not provided a sufficiently high attractive force nor also the ability to exhibit sufficiently low residual magnetic force necessary for effecting a release. For example, U.S. Pat. No. 3,406,837 discloses a work transfer device wherein the gripping mechanism may be a magnetic gripper for workpieces of magnetically-attracted ferrous metal and an ejector pin is used to eject the workpiece.
U.S. Pat. No. 3,878,596 discloses a workpiece assembly apparatus which incorporates a magnetic chuck on a robot arm and U.S. Pat. No. 4,287,459 discloses an industrial robot with a robot hand which may be an electromagnet.
U.S. Pat. No. 2,915,682 discloses a lifting magnet with a lifting surface of concentric and separated pole pieces and permanent magnet material movably mounted by a ratchet mechanism so that its flux may be directed into and out of a circuit including the pole pieces and a ferromagnetic payload.
U.S. Pat. No. 2,243,616 discloses a lifting magnet device having a cylindrically shaped permanent magnet mounted for rotation about its cylinder axis between a pair of soft iron pole pieces to a first rotary position which completes a magnetic circuit through a payload for lifting the same or to a second rotary position which effects its release. All of the above are characterized by either complex mechanisms and/or weak holding forces which are often inadequate.